Variable capacitance with delay lock loop

ABSTRACT

An integrated circuit includes a delay lock loop (DLL) circuit that generates incremental delay line signals and a delay line output signal based on a received clock signal. A pulse-width modulation (PWM) control module generates a PWM control signal. A variable capacitance circuit is controlled based on the delay line output signal, the PWM control signal, and one of the incremental delay line signals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/180,853, filed Jul. 28, 2008, which claims the benefit of U.S.Provisional Application No. 61/024,711, filed Jan. 30, 2008, and is acontinuation-in-part of U.S. patent application Ser. No. 12/114,479,filed on May 2, 2008, which is a continuation of U.S. patent applicationSer. No. 11/242,230 (now U.S. Pat. No. 7,375,597), filed on Oct. 3,2005, which claims the benefit of U.S. Provisional Application No.60/704,280, filed on Aug. 1, 2005, and U.S. Provisional Application No.60/722,732, filed on Sep. 30, 2005. The disclosures of the applicationsreferenced above are incorporated herein by reference.

FIELD

The present disclosure relates generally to electronic circuit tuning,and more particularly to pulse-width modulating capacitors to achievelow-noise, fine-frequency tuning.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Frequency responses of electronic circuits are tuned in variousapplications, such as wired or wireless switches, controllers,transceivers, filters, power management units, data storage units, etc.Current techniques used to tune a frequency response have limitedresolution and limited noise minimization control.

In addition, some tuning circuits tend to require additional terminalsand system board space. For example, tuning circuits with crystaloscillators are used for high accuracy and low temperature drift tuningapplications. A crystal oscillator, when used as a separate stand-alonedevice, is coupled to one or more pins of an integrated circuit andconsumes system board space.

To save system board space, varactor diodes may be used and included inan integrated circuit. However, when capacitance of a varactor diode istuned, such as by applying an analog control voltage in an open loopmanner, noise problems result. Although current of the integratedcircuit can be increased in order to reduce the noise, increased currentresults in increased power consumption. Increased power consumptiondecreases the working life of battery powered electronic systems.

Digitally adjusted capacitors, such as capacitors that are connected ordisconnected using a switch, can be used to reduce noise in a tuningcircuit. Digitally adjusted capacitors are typically either equally orbinarily weighted. When equally weighted, a large number of capacitorsand corresponding switches provide tuning with a large tuning range anda fine resolution. Where binarily weighted, capacitors with smallcapacitance values are limited in size by parasitic capacitances of theswitches. Capacitors with large capacitance values are limited byavailable die area.

SUMMARY

In one embodiment, an integrated circuit is provided and includes adelay lock loop (DLL) circuit. The DLL circuit generates incrementaldelay line signals and a delay line output signal based on a receivedclock signal. A pulse-width modulation (PWM) control module generates aPWM control signal. A variable capacitance circuit is controlled basedon the delay line output signal, the PWM control signal, and one of theincremental delay line signals.

In other features, the variable capacitance circuit includes acapacitance and a switch that enables current flow to the capacitancebased on the delay line output signal, the PWM control signal, and oneof the incremental delay line signals.

In other features, the integrated circuit includes a multiplexer thatgenerates a selected delay line signal based on the PWM control signaland one of the incremental delay line signals. In other features, thevariable capacitance circuit is controlled based on the selected delayline signal and the delay line output signal.

In other features, the integrated circuit includes a latch that enablescurrent flow to the variable capacitance circuit based on the delay lineoutput signal, the PWM control signal, and one of the incremental delayline signals.

In still other features, the integrated circuit includes a latch thatcontrols charging of the variable capacitance circuit based on the delayline output signal, the PWM control signal, and one of the incrementaldelay line signals.

In other features, the integrated circuit includes a multiplexer thatgenerates a selected delay line signal based on the PWM control signaland one of the incremental delay line signals. A latch generates anadjustment signal based on the selected delay line signal and the delayline output signal. A switch enables current flow to the variablecapacitance circuit based on the adjustment signal.

In yet other features, the PWM control module generates the PWM controlsignal based on a condition signal. In other features, the conditionsignal is generated based on a measurement of one of an environment anda process.

In other features, the DLL circuit includes a phase detector thatdetects the difference in phase between the received clock signal andthe delay line output signal. The delay line output signal is generatedbased on the phase difference. In other features, the DLL circuitincludes a filter that generates a filtered difference signal based onthe phase difference. The delay line output signal is generated based onthe filtered difference signal.

In further features, the integrated circuit includes a calibrationcontrol module that generates a calibration control signal based on thereceived clock signal. The PWM control module generates the PWM controlsignal based on the calibration control signal. In other features, thecalibration control module generates the calibration control signalbased on a reference clock signal. In other features, the calibrationcontrol module generates the calibration control signal based on atemperature signal.

In still other features, the integrated circuit includes a calibrationcontrol module that generates a calibration control signal based on atemperature signal. The pulse-width modulation circuit generates the PWMcontrol signal based on the calibration control signal.

In other features, the integrated circuit includes a divide-by-N modulethat divides the received clock signal to generate a divided clocksignal, where N is an integer greater than 0. The DLL circuit generatesthe incremental delay line signals and the delay line output signalbased on the divided clock signal.

In yet other features, the integrated circuit includes a divide-by-Nmodule that divides the received clock signal to generate a dividedclock signal, where N is an integer greater than 0. The PWM controlmodule generates the PWM control signal based on the divided clocksignal. In other features, the PWM control module generates the PWMcontrol signal based on the divided clock signal and a receivedcondition signal. In other features, the condition signal is generatedbased on a measurement of one of an environment and a process.

In further features, the PWM control module generates the PWM controlsignal based on entries in a lookup table. In other features, the PWMcontrol module generates the PWM control signal based on temperatureentries in the lookup table.

In other features, a method of operating an integrated circuit isprovided and includes generating incremental delay line signals and adelay line output signal based on a received clock signal. A PWM controlsignal is generated. A variable capacitance circuit is controlled basedon the delay line output signal, the PWM control signal, and one of theincremental delay line signals.

In other features, the method includes enabling current flow to acapacitance of the variable capacitance circuit based on the delay lineoutput signal, the PWM control signal, and one of the incremental delayline signals.

In still other features, the method includes generating a selected delayline signal based on the PWM control signal and one of the incrementaldelay line signals. In other features, the method includes controllingthe variable capacitance circuit based on the selected delay line signaland the delay line output signal.

In other features, the method includes enabling current flow to thevariable capacitance circuit based on the delay line output signal, thePWM control signal, and one of the incremental delay line signals.

In yet other features, the method includes charging the variablecapacitance circuit based on the delay line output signal, the PWMcontrol signal, and one of the incremental delay line signals.

In other features, the method includes generating a selected delay linesignal based on the PWM control signal and one of the incremental delayline signals. An adjustment signal is generated based on the selecteddelay line signal and the delay line output signal. Current flow isenabled to the variable capacitance circuit based on the adjustmentsignal.

In other features, the method includes generating the PWM control signalbased on a condition signal. In other features, the condition signal isgenerated based on a measurement of one of an environment and a process.

In further features, the method includes detecting difference in phasebetween the received clock signal and the delay line output signal. Thedelay line output signal is generated based on the phase difference.

In other features, the method includes generating a filtered differencesignal based on the phase difference. The delay line output signal isgenerated based on the filtered difference signal.

In other features, the method includes generating a calibration controlsignal based on the received clock signal. The PWM control signal isgenerated based on the calibration control signal. In other features,the calibration control signal is generated based on a reference clocksignal. In other features, the calibration control signal is generatedbased on a temperature signal.

In still other features, the method includes generating a calibrationcontrol signal based on a temperature signal. The PWM control signal isgenerated based on the calibration control signal.

In other features, the method includes dividing the received clocksignal to generate a divided clock signal via a divide-by-N module,where N is an integer greater than 0. The incremental delay line signalsand the delay line output signal are generated based on the dividedclock signal.

In yet other features, the method includes dividing the received clocksignal to generate a divided clock signal via a divide-by-N module,where N is an integer greater than 0. The PWM control signal isgenerated based on the divided clock signal.

In other features, the PWM control signal is generated based on thedivided clock signal and a received condition signal. In other features,the condition signal is generated based on a measurement of one of anenvironment and a process. In other features, the PWM control signal isgenerated based on entries in a lookup table. In other features, the PWMcontrol signal is generated based on temperature entries in the lookuptable.

In further features, an integrated circuit is provided and includes DLLmeans for generating incremental delay line signals and a delay lineoutput signal based on a received clock signal. Pulse-width modulationmeans generates a PWM control signal. Variable capacitance meansprovides a variable capacitance that is controlled based on the delayline output signal, the PWM control signal, and one of the incrementaldelay line signals.

In other features, the variable capacitance means includes capacitancemeans for providing a capacitance. Switching means enables current flowto the capacitance based on the delay line output signal, the PWMcontrol signal, and one of the incremental delay line signals.

In still other features, the integrated circuit includes multiplexingmeans for generating a selected delay line signal based on the PWMcontrol signal and one of the incremental delay line signals. In otherfeatures, the variable capacitance means is controlled based on theselected delay line signal and the delay line output signal.

In other features, the integrated circuit includes latching means forenabling current flow to the variable capacitance means based on thedelay line output signal, the PWM control signal, and one of theincremental delay line signals.

In yet other features, the integrated circuit includes latching meansfor controlling charging of the variable capacitance means based on thedelay line output signal, the PWM control signal, and one of theincremental delay line signals.

In other features, the integrated circuit includes multiplexing meansfor generating a selected delay line signal based on the PWM controlsignal and one of the incremental delay line signals. Latching meansgenerates an adjustment signal based on the selected delay line signaland the delay line output signal. Switching means enables current flowto the variable capacitance means based on the adjustment signal.

In other features, the pulse-width modulation means generates the PWMcontrol signal based on a condition signal. In other features, thecondition signal is generated based on a measurement of one of anenvironment and a process.

In further features, the DLL means includes phase detection means fordetecting the difference in phase between the received clock signal andthe delay line output signal. The delay line output signal is generatedbased on the phase difference.

In other features, the DLL means includes filtering means for generatinga filtered difference signal based on the phase difference. The delayline output signal is generated based on the filtered difference signal.

In other features, the integrated circuit includes calibration means forgenerating a calibration control signal based on the received clocksignal. The pulse-width modulation means generates the PWM controlsignal based on the calibration control signal.

In other features, the calibration control means generates thecalibration control signal based on a reference clock signal. In otherfeatures, the calibration control means generates the calibrationcontrol signal based on a temperature signal.

In still other features, the integrated circuit includes calibrationmeans for generating a calibration control signal based on a temperaturesignal. The pulse-width modulation means generates the PWM controlsignal based on the calibration control signal.

In yet other features, the integrated circuit includes divide-by-N meansfor dividing the received clock signal to generate a divided clocksignal, where N is an integer greater than 0. The DLL means generatesthe incremental delay line signals and the delay line output signalbased on the divided clock signal.

In other features, the integrated circuit includes divide-by-N means fordividing the received clock signal to generate a divided clock signal,where N is an integer greater than 0. The pulse-width modulation meansgenerates the PWM control signal based on the divided clock signal.

In other features, the pulse-width modulation means generates the PWMcontrol signal based on the divided clock signal and a receivedcondition signal. In other features, the condition signal is generatedbased on a measurement of one of an environment and a process.

In other features, the pulse-width modulation means generates the PWMcontrol signal based on entries in a lookup table. In other features,the pulse-width modulation means generates the PWM control signal basedon temperature entries in the lookup table.

In still other features, the systems and methods described above areimplemented by a computer program executed by one or more processors.The computer program can reside on a computer readable medium such asbut not limited to memory, non-volatile data storage and/or othersuitable tangible storage mediums.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the disclosure, are intended forpurposes of illustration only and are not intended to limit the scope ofthe disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic of a circuit having a frequency characteristictuned by a pulse-width modulated capacitor according to an embodiment ofthe present disclosure;

FIG. 2 is a block diagram of a free-running oscillation circuitaccording to an embodiment of the present disclosure;

FIG. 3 is a block diagram illustrating the free-running oscillationcircuit of FIG. 2 undergoing calibration;

FIG. 4A is a flowchart of a method of calibrating the free-runningoscillation circuit of FIG. 2, and FIG. 4B is a flowchart of a method ofcalibrating a circuit according to an embodiment of the presentdisclosure;

FIG. 5 is a more detailed block diagram of a free-running oscillationcircuit according to an embodiment of the present disclosure;

FIG. 6 is a flowchart illustrating the operation of the free-runningoscillation circuit of FIG. 5;

FIG. 7 is a schematic of an oscillator that may be used as theoscillator 510 in the free-running oscillation circuit of FIG. 5 or asan oscillator in other embodiments of the present disclosure;

FIG. 8 illustrates a control signal generator and pulse-width modulatorthat may be used as the control signal generator and pulse-widthmodulator of FIG. 5 or as a control signal generator and pulse-widthmodulator in other embodiments of the present disclosure;

FIG. 9 is a timing diagram illustrating the operation of the pulse-widthmodulator of FIG. 8; and

FIG. 10A is a functional block diagram of a hard disk drive;

FIG. 10B is a functional block diagram of a DVD drive;

FIG. 10C is a functional block diagram of a high definition television;

FIG. 10D is a functional block diagram of a vehicle control system;

FIG. 10E is a functional block diagram of a cellular phone;

FIG. 10F is a functional block diagram of a set top box;

FIG. 10G is a functional block diagram of a media player;

FIG. 10H is a functional block diagram of a VoIP player;

FIG. 11 is a block diagram of a free-running oscillation circuitincorporating a delay lock loop (DLL) circuit according to an embodimentof the present disclosure;

FIG. 12 is a block diagram illustrating the free-running oscillationcircuit of FIG. 11 undergoing calibration;

FIG. 13 is a flowchart illustrating a method of calibrating thefree-running oscillation circuit of FIG. 12 according to anotherembodiment of the present disclosure;

FIG. 14 is a block diagram of a free-running oscillation circuitincorporating a DLL circuit according to another embodiment of thepresent disclosure; and

FIG. 15 is a data flow diagram illustrating operation of thefree-running oscillation circuit of FIG. 14 according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the disclosure, its application, or uses. For purposesof clarity, the same reference numbers will be used in the drawings toidentify similar elements. As used herein, the phrase at least one of A,B, and C should be construed to mean a logical (A or B or C), using anon-exclusive logical or. It should be understood that steps within amethod may be executed in different order without altering theprinciples of the present disclosure.

As used herein, the term module refers to an Application SpecificIntegrated Circuit (ASIC), an electronic circuit, a processor (shared,dedicated, or group) and memory that execute one or more software orfirmware programs, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality.

Referring to FIG. 1 is a schematic of a circuit having a frequencyresponse or characteristic tuned by a pulse-width modulated capacitoraccording to an embodiment of the present invention. This figureincludes a circuit 110, transistor M1 120, and capacitor C1 130. Thecircuit 110 has a frequency response or characteristic that is at leastpartially determined by the effective capacitance value of the capacitorC1 130. The circuit 110, transistor 120, and capacitor 130 may beincluded on an integrated circuit. This figure, as with the otherincluded figures, is shown for exemplary purposes and does not limiteither the possible embodiments of the present invention or the claims.

The adjust signal on line 122 adjusts or controls the impedance oftransistor M1 120. When the level of the adjust signal on line 122 ishigh, and transistor M1 120 is on and connects capacitor C1 130 toground, in effect connecting capacitor C1 130 to the circuit 110. Whenthe adjust signal on line 122 is low, the impedance of transistor M1 120is high, allowing capacitor C1 130 to float, effectively disconnectingthe capacitor C1 130 from the circuit 110. When this capacitor isconnected to ground, it is at least partially responsible fordetermining a frequency characteristic of the circuit 110. Conversely,when the capacitor C1 130 is floating, it has a reduced effect on thisfrequency response or characteristic.

However, when the capacitor C1 130 is floating it is not completelyremoved or disconnected. Transistor M1 120 includes parasiticcapacitances, notably the drain-to-gate capacitance and the capacitanceof the drain-to-bulk diode, which remains in series with capacitor C1130 when transistor M1 120 is off. These parasitic capacitances limitthe minimum practical size of C1 130. This in turn limits the resolutionwith which the frequency characteristic of the circuit 110 can be tuned.

Accordingly, embodiments of the present invention adjust the size ofcapacitor C1 130 with a finer resolution by applying a switching signalhaving a variable duty cycle, specifically the adjust signal on line122. By varying the duty cycle of the adjust signal on line 122, thecapacitor C1 130 is connected to the circuit 110 part of the time, anddisconnected from the circuit 110 for the remainder. In this way, a dutycycle adjustment can be used to vary the effective size of capacitor C1130. That is, as the duty cycle increases and device M1 120 is on for agreater portion of time, the effective size of capacitor C1 130 isincreased, while as the duty cycle is decreased, device M1 120 conductsor is on for a shorter portion and the effective size of C1 130 isthereby reduced.

Thus, a frequency response or characteristic of the circuit 110 can beadjusted by varying the duty cycle of the adjust signal on line 122.However, it should be noted that changes in the frequency of the adjustsignal on line 122 by themselves do not have a first-order effect on theeffective capacitance provided by the capacitor C1 130.

During operation when M1 120 is on, the voltage V2 on line 134 (thedrain of M1 120) is near ground. When the adjust signal on line 122switches low thereby shutting off M1 120, the voltage V2 on line 134 isallowed to float. Accordingly, the voltage V2 on line 134 tracks changesin the voltage V1 on line 132. Later, when the adjust signal on line 122returns high and M1 120 conducts, the voltage V2 on line 134 is againforced to ground. If the voltage V2 on line 134 has floated from groundwhen device M1 120 turns on, charge is injected through C1 130 into thecircuit 110. This charge injection should be accounted for in the designof the circuit 110 and the timing of the adjust signal on line 122. Itshould also be noted that the drain-to-bulk diode might turn on andclamp the voltage V2 on line 134 when the capacitor C1 130 is allowed tofloat, specifically when the voltage V2 on line 134 floats below ground.This clamping can be minimized by ensuring that the signal swing at V1132 does not exceed a few hundred millivolts.

In a specific embodiment of the present invention, the circuit 110 is anoscillator that provides an oscillatory signal at a frequency that isdetermined at least in part by the effective value of the capacitor C1130. In this embodiment, the adjust signal on line 122 is opened andclosed at a frequency that is a sub-harmonic of the frequency of theoscillator. Accordingly, each time the transistor M1 120 closes orbegins to conduct, the voltage V2 on line 134 is near ground, thuslimiting the charge injection back into the oscillator.

In this exemplary figure, the circuit 110 receives an input signal online 112 and provides an output on line 114. In various embodiments ofthe present invention, there is no input signal 112, for example wherethe circuit 110 is an oscillator as described above. The input andoutput signals may use single-ended or differential signalingtechniques. Typically, lines in this and the other figures may be oneline, or a group of lines, such as a bus.

The capacitor C1 130 may be in parallel or in series with one or moreother capacitors that may or may not be connected to switches. Thecapacitor C1 130 may be a metal-sinker capacitor, a metal-to-metalcapacitor, or other type of capacitor. It may be one capacitor, or acombination of more than one individual capacitor. The transistor M1 120may be an n-channel MOS device as shown. Alternately it may be ap-channel MOS device, bipolar device, HFET, HBT, MESFET, or other typeof transistor. In other embodiments of the present invention, thetransistor M1 120 may be replaced by another type of switch such as apass or tri-state gate. Also, in some embodiments the switch and thecapacitor may be combined into a single composite structure. While thesefigures show a switch transistor coupled between a capacitor and ground,in various embodiments, the switch may be between the capacitor and thecircuit, between the capacitor and another node, such as a bias voltageor a supply voltage, or the switch and capacitor may be take on otherarrangements.

The circuit 110 may be an oscillator as previously described, a filter,or other circuit where a variable frequency response or characteristicis desired. One example of an oscillator incorporating an embodiment ofthe present invention is shown in the next figure.

FIG. 2 is a block diagram of a free-running oscillation circuitaccording to an embodiment of the present invention. This figureincludes an oscillator 210, pulse-width modulator 220, transistor M1230, and capacitor C1 240. The oscillator 210 generates a clock signalon line 212. The clock signal has a frequency that is determined atleast partially by the effective capacitance value provided by thecapacitor C1 240 and transistor M1 230.

A condition signal is received on line 222 by the pulse-width modulator220. This condition signal may be either a current or a voltage that isprovided or generated in response to an environmental, process, or othercondition or combination thereof. For example, the condition signal online 22 may be in response to a temperature, power supply voltage, orother environmental condition. Alternately, the condition signal on line222 may be in response to a process variation occurring during themanufacture of an integrated circuit that includes one or more of thecircuits in this figure. In other embodiments, the condition signal online 222 may be a control setting, for example, a voltage provided by apotentiometer. The condition signal 222 may be proportional to thecondition itself or it may have another relationship to the condition.For example, the condition signal may be a current or a voltage that isproportional to absolute temperature.

The pulse-width modulator 220 converts the condition signal on line 222into the adjust signal on line 224. Specifically, the pulse-widthmodulation circuit 220 varies the duty cycle of the adjust signal online 224 as a function of the condition signal received on line 222.

The transistor M1 230 turns on and off under control of the level of theadjust signal on line 224, thus alternately connecting and disconnectingthe capacitor C1 240 from the oscillator 210. The longer capacitor C1240 is connected to the oscillator 210, the greater the effectivecapacitance value of the capacitor C1 240. While only one capacitor C1240 and corresponding transistor M1 230 are shown, practical circuitstypically include several such capacitor-transistor combinations inparallel or in series with each other, the transistors (or otherswitches) under control of various adjust signals.

Again, in a specific embodiment of the present invention, the adjustsignal on line 224 is a sub-harmonic of the clock frequency on line 212.In this embodiment, the clock signal on line 212 clocks the pulse widthmodulation circuit 220. In one embodiment, the nominal frequency of theoscillator 210 is 1.280 GHz. This frequency is divided by a factor offour to 320 MHz, which is further divided by 32, resulting in afundamental frequency of 10 MHz for the adjust signal on line 224. Theduty cycle of this 10 MHz signal is then varied and provided as theadjust signal on line 224.

The relationship between the condition signal on line 222 and the adjustsignal on line 224 may be different in various embodiments of thepresent invention. That is, the pulse width modulation circuit 220 maybe configured such that the frequency of the clock signal on line 212tracks in the condition signal on line 222. Alternately, otherrelationships are possible. For example, the pulse width modulationcircuit 220 may be configured to provide a frequency for the clocksignal on line 212 that is stable over changes in the condition that ismeasured to generate the condition signal on line 222.

A specific embodiment of the present invention provides an oscillatorhaving a clock signal with a frequency that is stable over temperature.In order to achieve this, the oscillator first undergoes a calibrationprocess. Examples of such a calibration process are shown in the nexttwo figures.

FIG. 3 is a block diagram illustrating the free-running oscillationcircuit of FIG. 2 while it is undergoing calibration. This figureincludes an oscillator 310, reference oscillator 320, calibrationcontrol circuit 330, programmable lookup table 340, transistor M1 350,capacitor C1 360, and pulse width modulator circuit 370. The frequencyof oscillation of the oscillator 310 is determined at least in part bythe effective capacitance value provided by the capacitor C1 360.Typically, the oscillator 310, transistor M1 350, and capacitor C1 360are included on an integrated circuit, while the reference oscillator320 is separate. The calibration control circuit 330 and lookup table340 may or may not be included on the integrated circuit depending onthe exact implementation.

The reference oscillator 320 may be a crystal oscillator or otherperiodic source. Alternately, it may be such a source in conjunctionwith one or more frequency multipliers or dividers. The calibrationcontrol circuit 330 includes a frequency detector that compares thefrequency of the reference clock signal on line 322 to the frequency ofthe clock signal on line 312. From this information, the calibrationcontrol circuit 330 provides a control signal on line 332.

The calibration control circuit 330 varies the value of the controlsignal on line 332 in a manner depending on the relative frequencies ofthese input signals. When the frequency of the clock signal on line 312is tuned within an acceptable margin of error to the frequency of thereference clock signal on line 322, the control signal on line 332, orother data corresponding to the control signal on line 332, is stored inthe lookup table 340 along with the condition measurement. This processmay be repeated at several condition values or states, and for one ormore different conditions.

Once a number of control signal values and their corresponding conditionmeasurements are stored in the lookup table 340, the data can be readout and further processed, though in other embodiments of the presentinvention, data is processed when determined without first being storedin a lookup table 340. In one embodiment of the present invention, abest-fit curve is generated based on the data. In a specific embodiment,this curve is described by a second-order polynomial, though in otherembodiments of the present invention it may be a different type of curvehaving a different order. Alternately, the curve may be predefined wherethe data used to shift the curve, not to define it. Other variations orcombinations can also be used. After the data is fit to a curve, severalmore control signal data points can be interpolated between the measureddata points.

A processor that is external to the integrated circuit can perform thecurve fitting and interpolation. For example, a processor that is partof a test or manufacturing system can perform either or both of thesefunctions. Alternately, an on-chip processor can do either or both ofthese functions, or they may be shared between on-chip and off-chipprocessors.

The interpolated control signal values (or data corresponding to controlsignal values) can be stored in a lookup table or other memory. The datacan be addressed by the corresponding condition measurement value. Thislookup table can be the same lookup table 340 as is used to storecondition measurements and control signal values before curve fitting isdone. Alternately, another lookup table can be used. The lookup table orother memory used to store interpolated data is typically on-chip;though in other embodiments it can be off-chip.

In a specific embodiment of the present invention, an on-chip heatingcircuit is used to vary the temperature of an integrated circuit thatincludes a circuit to be calibrated. This heating circuit dissipates avariable amount of power in order to adjust die temperature; dietemperature being the measured condition. One such heating circuit canbe found in copending U.S. patent application Ser. No. 11/243,017,titled “On-Die Heating Circuit and Control Loop for Rapid Heating of theDie,” by Jody Greenberg and Sehat Sutardja, filed Sep. 3, 2005, which isincorporated by reference.

The control signal values required for the frequency of the oscillator310 to match the frequency of the reference oscillator 320 are storedfor a number of temperatures. The temperature can be measured, or thetemperature can be inferred given a specific level of power dissipationin the heater circuit. Since each temperature measurement costs money,embodiments of the present invention typically limit the number oftemperature data points taken. For example, in one embodiment, twotemperature data points are taken. An expected curve is used, where thetwo data points are used to shift and adjust the curve. In anotherembodiment of the present invention, five data points are used, and asecond-order polynomial curve is fit to the data. In other embodiments,other curve-fitting techniques and other number of data points can beused.

From this curve, a larger number of data points can be interpolated. Forexample, in the specific embodiment, temperature is converted from ananalog PTAT voltage to an 8-bit address using an 8-bit analog-to-digitalconverter. Accordingly, 256 data points are interpolated and stored in amemory or lookup table that is addressed by the digital conversion ofthe temperature. In other embodiments, converters having otherresolutions and memories having other numbers of addressable locationscan be used.

In operation, the temperature is measured, converted to a digitalsignal, and used to address a control signal value. The control signalvalue is used to generate a pulse-width modulated adjust signal, whichin turn varies a capacitor value that tunes the oscillator to thedesired frequency.

FIG. 4A is a flowchart of a method of calibrating the free-runningoscillation circuit of FIG. 2. A condition signal corresponding to anenvironmental, process, or other condition is received in step 400. Instep 405, a reference clock signal is received. In step 410, anoscillator clock frequency is received. The frequency of the referenceclock is compared to the frequency of the oscillator in step 415.

In step 420, it is determined whether the oscillator is operating at thecorrect frequency. Specifically, it is determined whether the frequencyof the oscillator clock signal is within a margin of error of thefrequency of the reference clock signal. If it is, the control signalvalue, or information corresponding to the control signal, can be storedwith the measured condition value in step 445.

If it is not, the comparison is used to generate a control signal instep 425. The control signal is used to generate an adjust signal havinga variable duty cycle in step 430. In step 435, the adjust signal isused to pulse-width modulate or vary a capacitance. The modulatedcapacitance changes the oscillator frequency in step 440. The oscillatorclock, with its new frequency, can then be received and compared to thereference clock.

When data is taken at each of the desired temperatures, the conditionvalues and corresponding data can be read in step 450. More data pointscan be interpolated, for example by use of curve fitting, in step 455.The interpolated control signal values can be stored in step 460.

While this calibration technique is well suited to calibrating afree-running oscillator, it may be used for other circuits as well. Onemethod that is applicable to many other circuits is shown in thefollowing figure.

FIG. 4B is a flowchart of a method of calibrating a circuit according toan embodiment of the present invention. In step 480, a condition is setand measured. For example, a temperature may be set using a heatingcircuit as described above. In step 482, a control signal that isrequired to achieve a desired outcome at the set condition isdetermined. In step 484, the condition measurement and required controlsignal data is stored. This data may be stored in an on-chip, oroff-chip memory, FIFO, lookup table, registers, or other storagelocations. Alternately, the data may be processed or further used inreal-time without being stored. Alternately, the condition measurementvalues may be inferred, and the required control signal data stored atlocations identified by those inferred values.

In step 486, it is determined whether data has been taken at the lastcondition. If it hasn't, the condition is set and measured again in step480. When data has been taken at each desired condition, the storedcondition measurements and required control signal data can be read instep 488. In step 490, additional control signal data points can beinterpolated. This may be done by fitting the stored data to a curve, orby other method. One or more processors can perform this curve fittingand interpolation, and these processors can be on-chip or off-chip.Alternately, on-chip and off-chip circuits or processors can share theprocessing workload. In step 492, the interpolated control signal datapoints are stored. Typically, this data is stored on-chip, though it maybe stored off-chip in various embodiments of the present invention. Forexample, the data may be stored in an on-chip lookup table or othermemory, where address locations are identified by values of thecondition signal.

Further refinements to the oscillator circuit shown in FIG. 2 may bedesirable in some embodiments of the present invention. For example, ahysteresis buffer can be used to clean up the oscillator output signal.Also, various frequency dividers may be used such that a desired clockfrequency is realized. Examples are described in the following twofigures.

FIG. 5 is a more detailed block diagram of a free-running oscillationcircuit according to an embodiment of the present invention. Thiscircuit includes an oscillator 510, buffer 520, dividers 530 and 540,pulse-width modulation circuit 550, transistor M1 560, capacitor C1 570,and control signal generator 580. The effective capacitance of thecapacitor C1 570 at least partially determines a frequency response orcharacteristic of the oscillator 510, for examples its oscillationfrequency. While only one capacitor C1 570 and corresponding transistorM1 560 is shown for simplicity, typical embodiments of the presentinvention included several such combinations in series or parallelcontrolled by various adjust signals.

The oscillator 510 provides an output oscillation signal to the buffer520. The buffer 520 gains and sharpens the edges of the output signalprovided by the oscillator 510, which is typically a low-amplitudesinusoid. The buffer 520 may also include hysteresis to provide asubstantially glitch free output.

The output of the buffer 520 is received by a divider circuit 530, whichdivides the frequency provided by the oscillator by a factor of “N.”This signal can further be divided by divider 540, which in this exampledivides the frequency by a factor of “M” to provide a signal Vosc online 542. In other embodiments, other frequency dividers and multipliersmay be used. These dividers may also be programmable.

The control signal generator circuit 580 receives a condition signal online 582. Again, this signal may be derived by the measurement of anenvironmental, process, or other type of parameter. The control signalgenerator circuit 580 provides a control signal on line 552 to thepulse-width modulator circuit 550. The pulse width modulator circuit 550provides an adjust signal on line 554 to the oscillator circuit. Thissignal has a duty cycle that is modulated as a function of the conditionsignal received on line 552.

The adjust signal on line 554 controls the impedance of transistor M1560, which connects and disconnects capacitor C1 570 from the oscillator510. Changes in the duty cycle of the adjust signal on line 554 variesthe effective capacitance of capacitor C1 570 seen by the oscillator510. This in turn varies its oscillation frequency, and thus thefrequency of the output signal Vosc on line 542.

FIG. 6 is a flowchart illustrating the operation of the free-runningoscillation circuit of FIG. 5. An oscillation signal is generated instep 610. In step 620, this oscillation signal is gained. This has theeffect of sharpening the edges and increasing the amplitude of theoscillation signal. In step 630, the frequency of the oscillation signalis divided. In step 640, a measurement of a condition is received. Asbefore, the condition may be an environmental, process, or other type ofcondition. The measurement received may be a voltage or current that isrelated to the condition. For example, a voltage proportional toabsolute temperature may be received.

In step 650, a lookup table entry is found using the measurement of thecondition. In step 660, an adjustment signal is generated using thelookup table entry and the divided-gained oscillation signal. Theadjustment signal is used to set the frequency of the oscillation signalin active 670.

The entries in the lookup table may be such that the resultingoscillation frequency remains constant over temperature. Alternately,they may be such that the resulting oscillation frequency has somerelationship to temperature. In other embodiments, other conditionsbesides temperature may be used in finding entries in the lookup table.Further, more than one condition may be used by various embodiments ofthe present invention. In other embodiments, other memories or storagecircuits can be used instead of a lookup table.

FIG. 7 is a schematic of an oscillator that may be used as theoscillator 510 in the free-running oscillation circuit of FIG. 5, or asan oscillator in other embodiments of the present invention. This figureincludes a bias current generator 700, an oscillator core (or tank)including transistors M1A 710 and M2A 720, load (or tank) inductors L1730 and L2 740, and pulse-width modulated capacitors C1 755, C2 765, andCN 775, as well as their corresponding transistors M1 750, M2 760, andMN 770. Only the pulse-width modulated capacitors connected to the drainof M2A 720 are shown: corresponding capacitors and transistors connectedto the drain of transistor M1 710 are omitted for clarity. The gates ofthe omitted corresponding transistors can be driven by the same signalsas transistors M1 750, M2 750, and MN 770, though they may be driven byother signals. Other capacitors that are not selectively coupled anddecoupled from the oscillator core are also typically connected to thedrains of M1A 710 and M2A 720. These capacitors have been omitted forclarity.

The frequency of oscillation of this circuit is determined by the valuesof the inductors and the effective capacitance values seen by thoseinductors. These capacitors may be connected or disconnected by theircorresponding transistors on a steady-state basis, or they may beswitched by a signal having a duty cycle under control of a pulse withmodulation circuit.

In one embodiment of the present invention, there are 16 capacitors andcorresponding transistors connected to the drain of M2A 720, and 16other capacitors connected to the drain of M1A 710. These transistorscan be equally weighted, and they can be switched under control of 4bits that are thermally decoded into 16 adjust signals. The signals canhave a duty cycle that is varied in increments of one thirty-second ofthe period of the adjust signals. In other embodiments, other numbers ofcapacitors may be used, and their values may be weighted in a differentmanner. For example, they may be binarily weighted, and four, eight, orthirty-two capacitors may be used. Further, the duty cycle may be variedin equal or unequal increments, and the number of increments may be moreor less than 32. For example, the duty cycle may be varied in eighths,sixteenths, or sixty-fourths of the adjust signal period. Alternately,non-binary numbers may be used for any of these parameters.

In one exemplary embodiment of the present invention, a maximumfrequency for the oscillation circuit is achieved when all capacitorsremain disconnected by their corresponding transistors. The frequency ofoscillation can be reduced by one quantum by applying an adjust signalhaving a minimum duty cycle to one transistor (or typically, onetransistor connected to a capacitor that is connected to the drain of M1A710 and one transistor connected to a capacitor that is connected tothe drain of M2A 720). The frequency of oscillation can further bereduced by increasing this duty cycle, until the transistor remains on,that is, until its adjust signal has a duty cycle of one.

Further decreases in oscillator frequency are achieved by applying anadjust signal having a minimum duty cycle to a second transistor whilethe first transistor remains fully on and the remaining transistorsremain off. Decreases in oscillator frequency can continue until alltransistors remained fully on, at which point a minimum oscillationfrequency is reached. The operation of one exemplary pulse-widthmodulator that provides signals such as these is shown in the next twofigures.

FIG. 8 is a control signal generator and pulse-width modulator that maybe used as the control signal generator and pulse-width modulator ofFIG. 5 or as a control signal generator and pulse-width modulator inother embodiments of the present invention. This figure includes acontrol signal generator made up of an analog-to-digital converter 810and lookup table 820, and a pulse-width modulator made up of a counter830 and decoder 840. In other embodiments of the present invention,other circuits can be used to implement the control signal generator andpulse-width modulator.

A condition signal is received on line 812 by the analog-to-digitalconverter 810. The analog-to-digital converter provides a digital wordthat is used to address the lookup table 820. The lookup table in turnprovides a control signal to the counter 830 and decoder 840.

The control signal MSBs provided by the lookup table 820 on line 822 tothe decoder 840 are decoded and provided as a number of adjust signalson lines 842. In one embodiment of the present invention, a thermometerdecoder is used. A thermometer decoder decodes binarily weighted bitsinto a number of equally weighted bits. The control signal LSBs on line824 provided to the counter 830 are used to control the duty cycle of atleast one of the adjust signals on lines 842, as is shown in the timingdiagram which follows.

FIG. 9 is a timing diagram illustrating the operation of the pulse-widthmodulator of FIG. 8. This figure includes a clock signal 910, adjust 1-3signals 920, adjust 4 signal 930, and adjust 5-8 signals 940. The stateof these signals represents one of 64 possible states for this exemplaryembodiment of the present invention.

In this example, the adjust 1-3 signals 920 remain high, while adjust5-8 signals 940 remain low. The adjust 4 signal 930 has a variablesignal that has a duty cycle of three-eighths. That is, it is high forthree cycles of the clock 910, and low for 5 clock cycles. In thisembodiment, the eight adjust signals are decoded from three bitsprovided by lookup table, while the duty cycle is controlled by anotherthree bits provided by lookup table. In a specific embodiment of thepresent invention, four bits are provided to the decoder for 16 adjustsignals, and five bits are provided to the counter, for 32 possible dutycycles. In this embodiment, there are 512 possible signal states, thatis, the capacitance of the tank circuit can be varied in 512 increments.

In this example, the effective capacitance can be reduced one quantum bychanging the duty cycle to one-fourth, or increased one quantum bychanging the duty cycle to one-half. In other embodiments, the periodmay be less than or more than 8 clock cycles, and more or less thaneight adjust signals may be generated.

The capacitance seen by the oscillator when the adjust 4 signal 930 ishigh is greater than when the adjust 4 signal 930 is low. Accordingly,the oscillator tries to alternately decrease and increase its frequency.This would cause frequency modulation of the clock. However, if theclock is divided by the same ratio or integer multiple thereof as thepulse width modulated frequency then the frequency modulation issubstantially cancelled.

Referring now to FIGS. 10A-10G, various exemplary implementations of thepresent invention are shown. Referring to FIG. 10A, the presentinvention may be embodied in a hard disk drive 1000. The presentinvention may implement either or both signal processing and/or controlcircuits, which are generally identified in FIG. 10A at 1002. In someimplementations, signal processing and/or control circuit 1002 and/orother circuits (not shown) in HDD 1000 may process data, perform codingand/or encryption, perform calculations, and/or format data that isoutput to and/or received from a magnetic storage medium 1006.

HDD 1000 may communicate with a host device (not shown) such as acomputer, mobile computing devices such as personal digital assistants,cellular phones, media or MP3 players and the like, and/or other devicesvia one or more wired or wireless communication links 1008. HDD 1000 maybe connected to memory 1009, such as random access memory (RAM), a lowlatency nonvolatile memory such as flash memory, read only memory (ROM)and/or other suitable electronic data storage.

Referring now to FIG. 10B, the present invention may be embodied in adigital versatile disc (DVD) drive 1010. The present invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 10B at 1012, and/or mass datastorage 1018 of DVD drive 1010. Signal processing and/or control circuit1012 and/or other circuits (not shown) in DVD 1010 may process data,perform coding and/or encryption, perform calculations, and/or formatdata that is read from and/or data written to an optical storage medium1016. In some implementations, signal processing and/or control circuit1012 and/or other circuits (not shown) in DVD 1010 can also performother functions such as encoding and/or decoding and/or any other signalprocessing functions associated with a DVD drive.

DVD drive 1010 may communicate with an output device (not shown) such asa computer, television or other device via one or more wired or wirelesscommunication links 1017. DVD 1010 may communicate with mass datastorage 1018 that stores data in a nonvolatile manner. Mass data storage1018 may include a hard disk drive (HDD) such as that shown in FIG. 10A.The HDD may be a mini HDD that includes one or more platters having adiameter that is smaller than approximately 1.8″, DVD 1010 may beconnected to memory 1019, such as RAM, ROM, low latency nonvolatilememory such as flash memory, and/or other suitable electronic datastorage.

Referring now to FIG. 10C, the present invention may be embodied in ahigh definition television (HDTV) 1020. The present invention mayimplement either or both signal processing and/or control circuits,which are generally identified in FIG. 10C at 1022, a WLAN interfaceand/or mass data storage of the HDTV 1020. HDTV 1020 receives HDTV inputsignals in either a wired or wireless format and generates HDTV outputsignals for a display 1026. In some implementations, signal processingcircuit and/or control circuit 1022 and/or other circuits (not shown) ofHDTV 1020 may process data, perform coding and/or encryption, performcalculations, format data and/or perform any other type of HDTVprocessing that may be required.

HDTV 1020 may communicate with mass data storage 1027 that stores datain a nonvolatile manner such as optical and/or magnetic storage devices.At least one HDD may have the configuration shown in FIG. 10A and/or atleast one DVD may have the configuration shown in FIG. 10B. The HDD maybe a mini HDD that includes one or more platters having a diameter thatis smaller than approximately 1.8″. HDTV 1020 may be connected to memory1028 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. HDTV 1020 also maysupport connections with a WLAN via a WLAN network interface 1029.

Referring now to FIG. 10D, the present invention implements a controlsystem of a vehicle 1030, a WLAN interface and/or mass data storage ofthe vehicle control system. In some implementations, the presentinvention implements a powertrain control system 1032 that receivesinputs from one or more sensors such as temperature sensors, pressuresensors, rotational sensors, airflow sensors and/or any other suitablesensors and/or that generates one or more output control signals such asengine operating parameters, transmission operating parameters, and/orother control signals.

The present invention may also be embodied in other control systems 1040of vehicle 1030. Control system 1040 may likewise receive signals frominput sensors 1042 and/or output control signals to one or more outputdevices 1044. In some implementations, control system 1040 may be partof an anti-lock braking system (ABS), a navigation system, a telematicssystem, a vehicle telematics system, a lane departure system, anadaptive cruise control system, a vehicle entertainment system such as astereo, DVD, compact disc and the like. Still other implementations arecontemplated.

Powertrain control system 1032 may communicate with mass data storage1046 that stores data in a nonvolatile manner. Mass data storage 1046may include optical and/or magnetic storage devices for example harddisk drives HDD and/or DVDs. At least one HDD may have the configurationshown in FIG. 10A and/or at least one DVD may have the configurationshown in FIG. 10B. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″.Powertrain control system 1032 may be connected to memory 1047 such asRAM, ROM, low latency nonvolatile memory such as flash memory and/orother suitable electronic data storage. Powertrain control system 1032also may support connections with a WLAN via a WLAN network interface1048. The control system 1040 may also include mass data storage, memoryand/or a WLAN interface (all not shown).

Referring now to FIG. 10E, the present invention may be embodied in acellular phone 1050 that may include a cellular antenna 1051. Thepresent invention may implement either or both signal processing and/orcontrol circuits, which are generally identified in FIG. 10E at 1052, aWLAN interface and/or mass data storage of the cellular phone 1050. Insome implementations, cellular phone 1050 includes a microphone 1056, anaudio output 1058 such as a speaker and/or audio output jack, a display1060 and/or an input device 1062 such as a keypad, pointing device,voice actuation and/or other input device. Signal processing and/orcontrol circuits 1052 and/or other circuits (not shown) in cellularphone 1050 may process data, perform coding and/or encryption, performcalculations, format data and/or perform other cellular phone functions.

Cellular phone 1050 may communicate with mass data storage 1064 thatstores data in a nonvolatile manner such as optical and/or magneticstorage devices for example hard disk drives HDD and/or DVDs. At leastone HDD may have the configuration shown in FIG. 10A and/or at least oneDVD may have the configuration shown in FIG. 10B. The HDD may be a miniHDD that includes one or more platters having a diameter that is smallerthan approximately 1.8″. Cellular phone 1050 may be connected to memory1066 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. Cellular phone1050 also may support connections with a WLAN via a WLAN networkinterface 1068.

Referring now to FIG. 10F, the present invention may be embodied in aset top box 1080. The present invention may implement either or bothsignal processing and/or control circuits, which are generallyidentified in FIG. 10F at 1084, a WLAN interface and/or mass datastorage of the set top box 1080. Set top box 1080 receives signals froma source such as a broadband source and outputs standard and/or highdefinition audio/video signals suitable for a display 1088 such as atelevision and/or monitor and/or other video and/or audio outputdevices. Signal processing and/or control circuits 1084 and/or othercircuits (not shown) of the set top box 1080 may process data, performcoding and/or encryption, perform calculations, format data and/orperform any other set top box function.

Set top box 1080 may communicate with mass data storage 1090 that storesdata in a nonvolatile manner. Mass data storage 1090 may include opticaland/or magnetic storage devices for example hard disk drives HDD and/orDVDs. At least one HDD may have the configuration shown in FIG. 10Aand/or at least one DVD may have the configuration shown in FIG. 10B.The HDD may be a mini HDD that includes one or more platters having adiameter that is smaller than approximately 1.8″. Set top box 1080 maybe connected to memory 1094 such as RAM, ROM, low latency nonvolatilememory such as flash memory and/or other suitable electronic datastorage. Set top box 1080 also may support connections with a WLAN via aWLAN network interface 1096.

Referring now to FIG. 10G, the present invention may be embodied in amedia player 1072. The present invention may implement either or bothsignal processing and/or control circuits, which are generallyidentified in FIG. 10G at 1071, a WLAN interface and/or mass datastorage of the media player 1072. In some implementations, media player1072 includes a display 1076 and/or a user input 1077 such as a keypad,touchpad and the like. In some implementations, media player 1072 mayemploy a graphical user interface (GUI) that typically employs menus,drop down menus, icons and/or a point-and-click interface via display1076 and/or user input 1077. Media player 1072 further includes an audiooutput 1075 such as a speaker and/or audio output jack. Signalprocessing and/or control circuits 1071 and/or other circuits (notshown) of media player 1072 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any othermedia player function.

Media player 1072 may communicate with mass data storage 1070 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 format or other suitablecompressed audio and/or video formats. The mass data storage may includeoptical and/or magnetic storage devices for example hard disk drives HDDand/or DVDs. At least one HDD may have the configuration shown in FIG.10A and/or at least one DVD may have the configuration shown in FIG.10B. The HDD may be a mini HDD that includes one or more platters havinga diameter that is smaller than approximately 1.8″. Media player 1072may be connected to memory 1073 such as RAM, ROM, low latencynonvolatile memory such as flash memory and/or other suitable electronicdata storage. Media player 1072 also may support connections with a WLANvia a WLAN network interface 1074.

Referring to FIG. 10H, the present invention may be embodied in a Voiceover Internet Protocol (VoIP) phone 1083 that may include an antenna1039. The present invention may implement either or both signalprocessing and/or control circuits, which are generally identified inFIG. 10H at 1082, a wireless interface and/or mass data storage of theVoIP phone 1083. In some implementations, VoIP phone 1083 includes, inpart, a microphone 1087, an audio output 1089 such as a speaker and/oraudio output jack, a display monitor 1091, an input device 1092 such asa keypad, pointing device, voice actuation and/or other input devices,and a Wireless Fidelity (Wi-Fi) communication module 1086. Signalprocessing and/or control circuits 1082 and/or other circuits (notshown) in VoIP phone 1083 may process data, perform coding and/orencryption, perform calculations, format data and/or perform other VoIPphone functions.

VoIP phone 1083 may communicate with mass data storage 502 that storesdata in a nonvolatile manner such as optical and/or magnetic storagedevices, for example hard disk drives HDD and/or DVDs. At least one HDDmay have the configuration shown in FIG. 10A and/or at least one DVD mayhave the configuration shown in FIG. 10B. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″. VoIP phone 1083 may be connected to memory 1085,which may be a RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. VoIP phone 1083 isconfigured to establish communications link with a VoIP network (notshown) via Wi-Fi communication module 1086. Still other implementationsin addition to those described above are contemplated.

Referring to FIG. 11, a block diagram of a free-running oscillationcircuit 1300 incorporating a DLL circuit 1302 is shown. The free-runningoscillation circuit 1300 is similar to the free-running oscillationcircuit of FIG. 3 in that it includes an oscillator 1304, a pulse-widthmodulation (PWM) control module 1306, a transistor 1308, a capacitor1310. The free-running oscillation circuit 1300 also includes the DLLcircuit 1302, as well as a multiplexer 1312 and a latch 1314. Note thatthe transistor 1308 may be part of or replaced with a switch or aswitching circuit.

The DLL circuit 1302 increases circuit clock signal resolution and is incommunication with the oscillator 1304 and the multiplexer 1312. The DLLcircuit 1302 is coupled to the multiplexer 1312 via delay line tapterminals 1316. The latch 1314 is in communication with the DLL circuit1302 and the multiplexer 1312. The latch 1314 controls the variablestate of the transistor 1308 based on signals received from the DLLcircuit 1302 and the multiplexer 1312. The latch 1314 may be a SR latchas shown or may be some other suitable latch or latching module.

The DLL circuit 1302 increases resolution and thus allows for finetuning of a received clock signal 1320 from the oscillator 1304. The DLLcircuit 1302 provides small incremental delay line signals 1322 that arebased on the clock signal 1320. The incremental delay line signals 1322may be referred to as taps TAPS_(1-x), where X is an integer thatrepresents the total number of taps. The clock signal 1320 has anassociated PWM period T for a given signal pulse. The multiplexer 1312selects one of the taps TAP_(S) for the given modulated period T, whereS is an integer value greater than zero (0) and less than or equal to X.Each tap has a corresponding initial pulse HIGH and/or ON state with awidth τ.

The tap selection is based on a PWM control signal 1324 generated by thePWM control module 1306. The resolution of the free-running oscillationcircuit 1300 is based on the pulse width τ divided by the modulatedperiod T (τ/T). When the tap TAP_(X) is selected, the free-runningoscillation circuit 1300 is operating in a full ON state. In the full ONstate the latch 1314 operates based on the PWM control signal 1324.

Referring to FIG. 12, a block diagram illustrating the free-runningoscillation circuit 1300 undergoing calibration is shown. A calibrationcontrol module 1330 is coupled between the oscillator 1304 and the PWMcontrol module 1306. The oscillator 1304 is referred to as a primaryoscillator for the described embodiment. Likewise, the clock signal 1320is referred to as a primary clock signal 1320. A lookup table 1332 is incommunication with the calibration control module 1330. In use, theprimary oscillator 1304 generates the primary clock signal 1320, whichis received along with a reference clock signal 1334 by the calibrationcontrol module 1330. The reference clock signal 1334 is generated by areference oscillator 1336. The calibration control module 1330 generatescalibration control signals 1410, 1411 that are received by the PWMcontrol module 1306 and may also be received by the lookup table 1332.Although the calibration control signals 1410, 1411 are shown asseparate signals, they may be provided via the same signal line. Assimilarly described above, the lookup table 1332 may receive a conditionsignal 1340.

The DLL circuit 1302 includes a phase comparator 1350, a low pass filter1352 and a delay line 1354, as well as a DLL circuit input 1356 andoutput 1358. The delay line 1354 delays the primary clock signal 1320and has cascaded delay buffers 1360, which are coupled in series. TheDLL circuit input 1356 is coupled to the primary oscillator 1304. TheDLL circuit input 1356 is coupled to the phase comparator 1350 and thedelay line 1354. The phase comparator 1350 compares phases of theprimary clock signal 1320 and output of the delay line 1354. The phasecomparator 1350 is coupled to the low pass filter 1352, which is in turncoupled to the delay line 1354. The DLL circuit output 1358 is coupledto the phase comparator 1350. Delay line tap terminals 1304 associatedwith each delay buffer 1360 are coupled to the multiplexer 1312.

Referring now also to FIG. 13, a flowchart illustrating a method ofcalibrating a free-running oscillation circuit is shown. The conditionsignal, 1340 corresponds to an environment, process, or other conditionand is received in step 1400. In step 1402, the reference clock signal1334 is received by the calibration control module 1330 from thereference oscillator 1336. In step 1404, the primary clock signal 1320is also received by the calibration control module 1330 from the primaryoscillator 1304.

A reference frequency of the reference clock signal 1334 is compared toa primary frequency of the primary clock signal 1320 in step 1406. Instep 1408, the calibration control module 1330 determines whether theprimary oscillator 1304 is operating at a correct frequency.Specifically, the calibration control module 1330 determines whether theprimary frequency is within a margin of error of the referencefrequency.

When the primary frequency is within the margin of error, the firstcalibration control signal 1410 is generated by the calibration controlmodule 1330 based on the determination in step 1412. The firstcalibration control signal 1410 is stored with the measured conditionvalue in the lookup table 1332. This process may be repeated for severalcondition values or states, and for one or more different conditions.

When data is taken at different temperatures, the first calibrationcontrol signal 1410 and the condition values and corresponding data canbe read in step 1414. More data points can be interpolated, for exampleby use of curve fitting, in step 1416. The interpolated control signalvalues can be stored in step 1418. While this calibration technique iswell suited to calibrate a free-running oscillator, it may be used forother circuits as well.

In step 1420, when the primary frequency is not within the margin oferror, the calibration control module 1330 generates the secondcalibration control signal 1411 based on the determination. In step1422, the PWM 1306 generates the PWM control signal 1324 based on thesecond control signal 1411. The PWM control signal 1324 has a variableduty cycle.

In step 1424, the delay line 1354 generates a delay line output signal1425 based on the primary clock signal 1320. The primary clock signal1320 is passed through the buffers 1360 to generate the delay lineoutput signal 1425. In step 1426, the primary clock signal 1320 iscompared with the generated delay line output signal 1425. The DLLcircuit 1302 determines the phase difference between the primary clocksignal 1320 and the delay line output signal 1425 and generates a phasedifference signal 1427. In step 1428, the phase difference signal 1427is filtered to generate a filtered phase difference signal 1429, whichis provided to a delay line 1354. In step 1430, the filtered phasedifference signal 1429 is used as a loop control voltage, which isprovided to the buffers 1360. Control may return to step 1424 uponcompletion of step 1430 and iteratively perform steps 1424-1430 toupdate the loop control voltage.

In step 1432, the PWM control signal 1324 is used to select a tap of thedelay line 1354. For example only, the PWM control signal 1324 may be adigital control signal. The multiplexer 1312 selects a tap based on thePWM control signal to provide a selected delay line signal 1433 based onthe selected taps in step 1434.

In step 1436, the latch 1314 generates an adjustment signal 1437 basedon the delay line combined signal 1433 and the delay line output signal1425. The capacitor 1310 is modulated to change the primary frequencybased on the adjustment signal 1437, in step 1438. The above steps maybe repeated with a new primary clock signal. The frequency of the newprimary clock signal may be received and compared to a reference clocksignal through repetition of the steps 1404-1408 and 1420-1438 and/orperformance of the steps 1412-1418.

Referring to FIG. 14, a more detailed block diagram of a free-runningoscillation circuit 1500 incorporating a DLL circuit 1502 is shown. Thefree-running oscillation circuit 1500 is similar to the free-runningoscillation circuit of FIG. 5 in that it includes an oscillator 1502, abuffer 1504, a divide by N module 1506, a divide by M module 1508, a PWMcontrol module 1510, a transistor 1512, a capacitor 1514, and a controlsignal generator 1516. The free-running oscillation circuit 1500 alsoincludes the DLL circuit 1502, as well as a multiplexer 1518 and a latch1520. The multiplexer 1518 and the latch 1520 are part of a DLLselection circuit 1521.

The DLL circuit 1502 includes a phase comparator 1522, a low pass filter1524 and a delay line 1526 and has a DLL circuit input 1528 and output1530. The phase comparator 1522 is coupled to the low pass filter 1524,which is in turn coupled to the delay line 1526, which has cascadedbuffers 1527. The DLL circuit input 1528 is coupled to the divide by Nand M modules 1506, 1508. The DLL circuit output 1530 is coupled to thelatch 1520. The multiplexer 1518 selects one of tap outputs 1531 of thedelay line 1526 based on a PWM control signal 1532 from the PWM controlmodule 1510. The latch 1520 may be set and reset based on the selectedtap outputs and a delay line output signal 1534 from the delay lineoutput 1530.

The oscillator 1502 provides a primary clock signal 1540 to the buffer1504. The buffer 1504 adjusts the amplitude and sharpens the edges ofthe primary clock signal 1540 provided by the oscillator 1502. Thebuffer 1504 may have a hysteresis characteristic to provide asubstantially glitch free output signal.

A buffered oscillation signal 1542 out of the buffer 1504 is received bythe divide by N module 1506. The divide by N module 1506 divides thefrequency of the buffered oscillation signal 1542 by a factor of N togenerate a divided clock signal 1544. The divided clock signal 1544 isreduced in frequency relative to the buffered oscillation signal 1542.The frequency of the divided clock signal 1544 may be further divided bythe divide by M module 1508, which in turn generates an output signalV_(osc). In other embodiments, other frequency dividers and multipliersmay be used, These dividers may also be programmable.

The control signal generator 1516 receives a condition input signal1546. The condition input signal 1546 may be derived by the measurementof an environment, process, or other type of parameter. The controlsignal generator 1516 generates a condition control signal 1548 based onthe condition input signal 1546. The condition control signal 1548 maybe stored in a lookup table 1547.

The PWM control module 1510 provides the PWM control signal 1532 to themultiplexer 1518. The PWM control signal 1532 may be generated based onthe condition input signal 1546. The PWM control module 1510 may accessinformation stored in the lookup table 1547. The PWM control module 1510may generate the PWM control signal 1532 based on calibrationinformation stored in the lookup table 1547. The calibration informationmay be stored in the lookup table 1547 during a calibration period andlater accessed during operation. For example, calibration informationthat is stored based on calibration control signals, such as thecalibration control signals 1410, 1411 of FIG. 12, may be stored in thelookup table 1547 and used when generating the PWM control signal 1532.The PWM control module 1510 may also or alternatively generate the PWMcontrol signal 1532 based on condition information stored in the lookuptable 1547 by the control signal generator 1516.

The latch 1520 generates an adjustment signal 1550 that controls theimpedance of transistor 1512, which connects and disconnects capacitor1514 from the oscillator 1502. Changes in the duty cycle of theadjustment signal 1550 varies the effective capacitance of the capacitor1514, as seen by the oscillator 1502. This in turn varies theoscillation frequency of the oscillator 1502, and thus the frequency ofthe output signal V_(osc). For this reason the transistor 1512 and thecapacitor 1514 in combination form a variable capacitance circuit 1552that receives the adjustment signal 1550 as an input signal.

Referring now also to FIG. 15, a data flow diagram illustrating theoperation of the free-running oscillation circuit 1500 is shown. Theprimary clock signal 1540 is generated in step 1600. In step 1602,amplitude of the primary clock signal 1540 is adjusted via the buffer1504. This has the effect of sharpening the edges and increasing theamplitude of the primary clock signal 1540 to generate the bufferedoscillation signal 1542. In step 1604, the frequency of the bufferedoscillation signal 1542 is divided to generate the divided clock signal1544, which is a frequency reduced relative to the buffered oscillationsignal 1542. In step 1606, a measurement of a condition may be receivedand/or stored in the lookup table 1547. For example, the condition inputsignal 1546 may be received by the control signal generator 1516.

In step 1608, the lookup table 1547 may be accessed to obtaincalibration and/or condition information. In step 1610, the PWM controlsignal 1532 may be generated based on information from the lookup table1547 and based on the divided clock signal 1544. In step 1612, the delayline output signal 1534 is generated based on the divided clock signal1544.

In step 1614, the divided clock signal 1544 is compared with thegenerated delay line output signal 1534. The DLL circuit 1502 determinesthe phase difference between the divided clock signal 1544 and the delayline output signal 1534 and generates a phase difference signal 1615. Instep 1616, the phase difference signal 1615 is filtered to generate afiltered phase difference signal 1617, which is provided to the delayline 1526.

In step 1618, the filtered phase difference signal 1617 is used as aloop control voltage, which is provided to the buffers 1527 of the delayline 1526. Control may return to step 1612 upon completion of step 1618and iteratively perform steps 1612-1618 to update the loop controlvoltage.

In step 1620, the PWM control signal 1532 is used to select tap outputsof the delay line 1526, which is based on the frequency reduced clocksignal 1544. In step 1622, a delay line combined signal 1623 isgenerated based on the selected tap outputs.

In step 1624, an adjustment signal, such as the adjustment signal 1550,is generated based on the delay line combined signal 1623 and the delayline output signal 1534. The adjustment signal 1550 is used to set thefrequency of the primary clock signal 1540 in step 1626. Control mayreturn to step 1600 upon completion of step 1626 and iteratively performsteps 1600-1626. The steps 1600-1626 may be repeated with a new primaryclock signal. The frequency of the new primary clock signal may bereceived and compared to a reference clock signal.

The above-described steps described with respect to the embodiments ofFIGS. 4, 6, 13 and 15 are meant to be illustrative examples; the stepsmay be performed sequentially, synchronously, simultaneously, or in adifferent order depending upon the application.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification,and the following claims.

What is claimed is:
 1. An oscillation circuit comprising: a delay lockloop circuit configured to generate (i) a plurality of incremental delayline signals and (ii) a delay line output signal, wherein the pluralityof incremental delay line signals and the delay line output signal aregenerated based on a clock signal received from an oscillator; apulse-width modulation control module configured to generate apulse-width modulation control signal; a tunable circuit configured toadjust operation of the oscillator, the tunable circuit comprising atransistor having a control terminal, a first terminal and a secondterminal, the transistor configured to provide a variable impedanceacross the first terminal and the second terminal thereof based on anadjustment signal input to the control terminal, and a capacitance incommunication with the oscillator and one of the first and secondterminals; and a delay line selection circuit configured to generate theadjustment signal based on (i) the delay line output signal, (ii) thepulse-width modulation control signal, and (iii) one of the incrementaldelay line signals.
 2. The oscillation circuit of claim 1, wherein thedelay line selection circuit comprises: a multiplexer configured toselect one of the plurality of incremental delay line signals based onthe pulse-width modulation control signal; and a latch configured togenerate the adjustment signal based on (i) the selected one of theplurality of incremental delay line signals, and (ii) the delay lineoutput signal.
 3. The oscillation circuit of claim 1, wherein thetransistor adjusts current flowing to the capacitance based on theadjustment signal.
 4. The oscillation circuit of claim 1, wherein thedelay line selection circuit is configured to adjust a charging time ofthe tunable circuit.
 5. The oscillation circuit of claim 1, wherein thepulse-width modulation control module generates the pulse-widthmodulation control signal based on a condition signal.
 6. Theoscillation circuit of claim 5, wherein the condition signal isgenerated based on a measurement of at least one of an environment and aprocess.
 7. The oscillation circuit of claim 1, wherein: the delay lockloop circuit comprises a phase detector configured to detect adifference in phase between the received clock signal and the delay lineoutput signal; and the delay line output signal is generated based onthe phase difference.
 8. The oscillation circuit of claim 7, wherein:the delay lock loop circuit further comprises a filter configured togenerate a filtered difference signal based on the phase difference; andthe delay line output signal is generated based on the filtereddifference signal.
 9. The oscillation circuit of claim 1, furthercomprising a calibration control module configured to generate acalibration control signal based on the received clock signal, whereinthe pulse-width modulation control module generates the pulse-widthmodulation control signal based on the calibration control signal. 10.The oscillation circuit of claim 9, wherein the calibration controlmodule generates the calibration control signal based on a referenceclock signal.
 11. The oscillation circuit of claim 9, wherein thecalibration control module generates the calibration control signalbased on a temperature signal.
 12. The oscillation circuit of claim 1,further comprising: a calibration control module configured to generatea calibration control signal based on a temperature signal, wherein thepulse-width modulation control module generates the pulse-widthmodulation control signal based on the calibration control signal. 13.The oscillation circuit of claim 1, further comprising: a divide-by-Nmodule configured to divide the received clock signal to generate adivided clock signal, where N is an integer greater than 1, wherein thedelay lock loop circuit generates the plurality of incremental delayline signals and the delay line output signal based on the divided clocksignal.
 14. The oscillation circuit of claim 1, further comprising: adivide-by-N module configured to divide the received clock signal togenerate a divided clock signal, where N is an integer greater than 1,wherein the pulse-width modulation control module generates thepulse-width modulation control signal based on the divided clock signal.15. The oscillation circuit of claim 14, wherein: the pulse-widthmodulation control module generates the pulse-width modulation controlsignal based on (i) the divided clock signal, and (ii) a receivedcondition signal, and wherein the condition signal is generated based ona measurement of at least one of an environment and a process.
 16. Theoscillation circuit of claim 1, wherein: the pulse-width modulationcontrol module generates the pulse-width modulation control signal basedon entries in a lookup table, and the pulse-width modulation controlmodule generates the pulse-width modulation control signal based ontemperature entries in the lookup table.
 17. An oscillation circuitcomprising: a delay lock loop circuit configured to generate (i) aplurality of incremental delay line signals and (ii) a delay line outputsignal, wherein the plurality of incremental delay line signals and thedelay line output signal are generated based on a clock signal receivedfrom an oscillator; a pulse-width modulation control module configuredto generate a pulse-width modulation control signal; a tunable circuitconfigured to adjust operation of the oscillator, the tunable circuitcomprising a capacitance in communication with the oscillator, and afirst circuit in communication with the oscillator and configured toadjust current supplied to the capacitance based on an adjustmentsignal; and a delay line selection circuit configured to generate theadjustment signal based on (i) the delay line output signal, (ii) thepulse-width modulation control signal, and (iii) one of the incrementaldelay line signals.
 18. The oscillation circuit of claim 17, wherein thedelay line selection circuit comprises: a multiplexer configured toselect one of the plurality of incremental delay line signals based onthe pulse-width modulation control signal; and a latch configured togenerate the adjustment signal based on (i) the selected one of theplurality of incremental delay line signals, and (ii) the delay lineoutput signal.
 19. A circuit comprising: a delay lock loop circuitconfigured to generate (i) a plurality of incremental delay line signalsand (ii) a delay line output signal, wherein the plurality ofincremental delay line signals and the delay line output signal aregenerated based on a clock signal received from an oscillator; apulse-width modulation control module configured to generate apulse-width modulation control signal; a tunable circuit configured toadjust operation of the oscillator, the tunable circuit comprising acapacitance in communication with the oscillator, and a variableimpedance circuit in communication with the oscillator, wherein thevariable impedance circuit is configured to vary an impedance of thevariable impedance circuit based on an adjustment signal; and a delayline selection circuit configured to generate the adjustment signalbased on (i) the delay line output signal, (ii) the pulse-widthmodulation control signal, and (iii) one of the plurality of incrementaldelay line signals, wherein the delay line selection circuit includes adevice, and wherein the device is configured to receive (i) the delayline output signal, and (ii) a selected one of the plurality ofincremental delay line signals.
 20. A circuit comprising: a delay lockloop circuit configured to generate (i) a plurality of incremental delayline signals and (ii) a delay line output signal, wherein the pluralityof incremental delay line signals and the delay line output signal aregenerated based on a clock signal received from an oscillator; apulse-width modulation control module configured to generate apulse-width modulation control signal; a tunable circuit configured toadjust operation of the oscillator, the tunable circuit comprising acapacitance in communication with the oscillator, and a variableimpedance circuit in communication with the oscillator, wherein thevariable impedance circuit is configured to vary an impedance of thevariable impedance circuit based on an adjustment signal; and a delayline selection circuit configured to generate the adjustment signalbased on (i) the delay line output signal, (ii) the pulse-widthmodulation control signal, and (iii) one of the plurality of incrementaldelay line signals, wherein the delay line selection circuit comprises amultiplexer configured to select one of the plurality of incrementaldelay line signals based on the pulse-width modulation control signal;and a latch configured to generate the adjustment signal based on (i)the selected one of the plurality of incremental delay line signals, and(ii) the delay line output signal.
 21. A circuit comprising: a delaylock loop circuit configured to generate (i) a plurality of incrementaldelay line signals and (ii) a delay line output signal, wherein theplurality of incremental delay line signals and the delay line outputsignal are generated based on a clock signal received from anoscillator; a pulse-width modulation control module configured togenerate a pulse-width modulation control signal; a tunable circuitconfigured to adjust operation of the oscillator, the tunable circuitcomprising a capacitance in communication with the oscillator, and avariable impedance circuit in communication with the oscillator, whereinthe variable impedance circuit is configured to vary an impedance of thevariable impedance circuit based on an adjustment signal, wherein thevariable impedance circuit comprises a transistor, wherein thetransistor comprises a control terminal, and wherein the controlterminal is configured to receive the adjustment signal; and a delayline selection circuit configured to generate the adjustment signalbased on (i) the delay line output signal, (ii) the pulse-widthmodulation control signal, and (iii) one of the plurality of incrementaldelay line signals.